Mill control



Nov. 15, 1938. a RQDER 2,136,907

MILL CONTROL Filed May 1'7, 1957 2 Sheets-Sheet 1 5 5 s 1 4 Q $6 a 4INVENTOR (07/ Wade/1X [p06 Flier ATTORNEYS Nov. 15, 1938. L RQDER2,136,907

MILL CONTROL Filed May 17; 1937 2 Sheets-Sheet 2 lNVENTOR PM, ba J, -wp

ATTORNEYS Patented Nov. 15, 1938 UNITED STATES PATENT OFFICE assignor toF. L. Smidth 8: Company,

New

York, N. Y., a corporation of New Jersey Application May 1'7, 1937,Serial No. 143,111 In Great Britain May 18, 1936 1 Claim.

This invention relates to grinding or crushing installations and isparticularly applicable to tube mills and ball mills.

It is well-known that a grinding or crushing 5 mill operatesinefilciently and uneconomically ii there is any departure from theoperating con ditions for which it was designed. In particular, if thematerial is fed to the mill at too high a rate the operation isinefilcient, and it it is led to the mill too slowly there is notsuflicient ma terial for the grinding elements to act upon and then agreat deal of their work is converted into heat owing to impact andfriction between the grinding elements themselves. Other factors whichdetermine the output of the mill are the speed at which it is driven andthe fineness of the material, but as a rule the quantity of material fedin a given time is the most important factor.

When the mill has been fed too quickly or too slowly for a certain timethe fact can, of course, be ascertained, for example by examining thedegree of fineness of the ground product leaving the mill. As however,this is not discovered until the grinding of the material has beenfinished, the feeding of the material to the mill and the operation ofthe mill have actually been irregular for some considerable time.

It is therefore a matter of great importance to be in a position toascertain as quickly as possible whether the feeding of material to themill has been irregular. It has been found by experience that skilledoperatives who are accustomed to superintending the running of mills areable to decide to some extent from the sound of the mill in operationwhether the mill is operating with too much or too little material, because a mill charged with too much material gives out a dull andsomewhat muilled sound. while a mill which is fed too slowly makes morenoise. Thus the attendant looking after the mill is able to adjust thefeed device so as to maintain a constant feed of material to the mill ata rate which is, within limits, the most suitable for the mill.

According to the present invention, a device responsive to the noisecaused by the grinding in a tube mill or ball mill is combined with themill. The device either affords a direct indication of the noise so thatthe attendant can regulate manually another device by which theoperation of the mill is influenced, or the device responsive to thenoise is arranged automatically to control said other device. It ispreferred that said other device should be a feed device, because ingeneral, for maximum efliclency of grinding, the mill should be run at agiven speed and should be fed only with as much material as it can.grind. However, a mill is able to increase its output when the speed of.revolution is increased within certain limits. The efliciency of themill may decrease when the mill speed is accelerated, as at the sametime the power consumption will increase, but if the speed is notincreased too much the output will increase. Thus the said other devicemay be a motor that drives the mill. When the mill motor thus isautomatically controlled, any increase in the mill feed will result inthe noise-meter indicating a less intense noise.

As stated above, the output of the mill is also determined by thefineness of the material, and small variations in the fineness willcause small variations in the output. It, therefore, the feed to thetube mill for some reason or other is increased the output may beincreased accordingly if the material is removed from the mill in asomewhat coarser state. Such adjustment of the fineness of material caneasily be eilectecl in mills which are air-swept, i. e. mills in whichthe fine particles are picked up and carried out of the mill by an airstream. When the velocity of the air-stream is increased the particleswhich are removed by the stream are coarser and vice versa. Thus thesaid other device may also be a fan or the equivalent thereof by whichthe current of air is caused to flow through the mill.

In practicing the invention, the physical or electro-mechanical impulseor series of impulses caused by the noise of grinding is convenientlyemployed. Various forms of. noise-meters are already known in which thenoise to be measured is converted into physical impulse, the magnitudeof which affords a measiue of the intensity 0! the noise. For example,such an instrument may consist oi a microphone with an amplifier (and,if desired. a detector) connected to a moving coil deflecting instrumentin such way that the deflection is proportional to the intensity of thesound received by the microphone. such noise-meters can be designed tobe sensitive to certain ranges of. audio ire uencles, and may preferablybe arranged to operate upon the range of frequencies in which thevariations in noise level occur in each per case. The use of such noisemeter in combination with the mill makes it possible to adjust theoperation of the mill, so that the noise remains constant, that is tosay, of a predetermined average level or magnitude.

Instead of utilizing the physical impulse generated by the noise, forexample an electro-mechanical impulse, to afford a measurement of thenoise so that the attendant can adjust the operation of the millaccordingly, it may be arranged for the said impulse or series ofimpulses to cause automatic adjustment of the device controlling themill operation, for example, by arranging for the electro-mechanicalimpulse to control the speed governor of the feed device.

In order that the invention may be clearly understood and readilycarried into effect, some embodiments of the invention will now bedescribed by way of example with reference to the accompanying drawings,in which Fig. 1 shows diagrammatically a microphone with a noise-metercombined with a tube mill so as to provide an indication of the noiseset up by the grinding in the mill for the guidance of the attendant;

Fig. 2 is a circuit diagram showing how the feed device of the mill maybe adjusted automatically; and

Figs. 3 and 4 illustrate modifications of the system of Fig. 2, whereinarrangements are provided to prevent over-control or hunting.

Fig. 1 illustrates a tube mill l enclosed in a casing 2 made ofsound-insulating material. Enclosing each mill in a separatesound-insulating casing avoids or reduces the noise nuisance in millinstallations. Additionally, the use of such stationary sound-insulatingcasings provides conditions in which the use of the present invention isparticularly favorable, since the microphone 3 is mounted inside thecasing 2 and consequently is not afiected by the noise from other millsin the room. The microphone may be placed at a point where the noise isparticularly intense, preferably close to the inlet end of the mill. Themicrophone 2 is connected by means of conductors 4 to a noise-meter I,which may be of known construction. The regulator 8 for the feed device(not shown) of the mill is placed close to the noise-meter 5 so that theattendant may observe the dial of the noise-meter, and according to thereading of this instrument as indicated by the pointer 8 may regulatethe feed of material to the mill by means of the manual regulator 6.

In the conductors 4 between the microphone 2 and the meter 5 there maybe connected an amplifier l and a tone filter 3|. The amplifier which ispreferably of the vacuum tube type customarily employed for audiofrequencies, raises the signal level sufiiciently to enable the use of aless sensitive and more rugged meter 5. It is also especially desirablein connection with the automatic control later to be described. The tonefilter 30 may comprise inductive, capacitive and resistive elementsconnected either as a band-pass filter or as a high-frequency orlowfrequency filter or a combination thereof, the purpose being toselect from the noise picked up by the microphone, and to pass to thecontrol meter 6 only those frequencies most faithfully representing theconditions in the mill on which the feed rate must be based. Todetermine these frequencies empirically it is preferable that some ofthe filter elements be adjustable.

Although it is not illustrated in detail in the drawings, a detector orrectifier may be interposed between the tone illter, if any, and .themeter 5. The box 30 may be considered to include the filter, thedetector, or both. If the detector is included a direct-currentinstrument may be employed of which the response is more nearlyproportional to the sound intensity being measured.

A scheme for automatic adjustment of the feed device of the mill isillustrated diagrammatically in Fig. 2, in which the microphone I isagain connected to the noise meter by means of conductors 4, in which anamplifier I and the tone filter 80,, are interposed in the conductors asin Fig. 1. In this arrangement the noise-meter i of Fig. 1 is replacedby one in which the pointer I has a movable contact 8 mounted on it andis arranged to come into contact with one of two stationary contacts l0and Ill, when the noise made by the mill increases or decreases to apredetermined extent and thereby causes the pointer 8 to make a sumcientdeflection. As a result, one or the other of two circuits is completeddepending on which of the stationary contacts II or III is touched bythe movable contact I.

If the rate of feed to the mfll exceeds a predetermined maximum, themill makes less noise than normally. It may be assumed that the pointer8 then turns to the left, bringing its contact 9 against the contact IIand thus completing a circuit from the supply ll, 20, through theconductor II. A time-lag relay ll included in this circuit operates,when the circuit has remained closed for a preselected time, to closeanother circuit including the source of supply 2|, 2! which is completedthrough a solenoid or electro-magnet l2 of a heavier relay. The armatureor plunger of the latter relay is then drawn up and by means of itscontact discs II completes a circuit from the power supply 2!, 22,through the motor ll, which is thus started. In the drawings, the motorI4 is shown diagrammatically connected by a driving chain II to theregulator 6 for the feed device to the mill, and in this case, theregulator l is turned to the left, for example, to reduce the rate offeed of material to the null. The charge of material in the mill is thenquickly decreased so that the noise set up is increased and then thepointer I is restored again to a position in which the contact 0 liesbetween the fixed contact I0 and III. This results in stopping the motorI and the regulator 0.

If, on the other hand, the charge of material in the mill should be toosmall, the sound level from the mill is increased and the pointer 8 willthen be deflected to the right making contact with the fixed contact l0and completing a circuit from the supply I9, 20, through anothertime-lag relay ll. Upon the closing of the contacts of the relay H asimilar circuit from the supply 2|, 22, is completed through anothersolenoid or electro-magnet l2, the contact discs ii of which complete acircuit from the power supply 2|, 22 with reversed polarity to the motorH. The motor will therefore start, but this time in the oppositedirection, so that the regulator 6 turns to the right increasing thespeed of the feed device and thus the rate of feed of material to themill.

The relays l1, H are time-lag relays in order to avoid operation of theregulating device 0 due to merely casual or temporary variations in thenoise made by the mill. There are several known types of time-lag relayswhich would be suitable for this purpose, the relays illustrated beingof the adjustable bi-metallic thermal type. As already mentioned, theserelays I1, ll, prevent the motor from being started until a preselectedtime after the contact 9 has reached the contact II or II so that casualvariations in the noise intensity will not cause the regulator 6 to beshifted, for so long as the contact In or ID remains closed.

An adjusting screw I8 is provided for rotating the disc carrying thecontacts l0, l, relatively to the contact 9 to enable the zero positionof the noise-meter to be adjusted. This permits a the noise intensity towhich the feed to the mill is responsive to be adjustably predetermined.

Fig. 3 differs from Fig. 2 only in the addition of a device to preventover-regulation and the setting up of a hunting eflect. This deviceoperates so that the electro-magnets l2, l2 when attracted will remainenergized for only a relatively short time and will then fall back tothe unattracted position. If, however, the contacts 9 and ID or IIIcontinue to be closed the electromagnets l2, l2 are again energizedthereby giving a series of short regulating periods. More specifically,the device may comprise an oiland-on relay, well known in the art, suchas is usually operated by a synchronous, alternating current clockmotor. In Fig. 3 this relay is designated 23 and comprises a synchronousalternating current clock motor 26 which operates adjustable timing cams21. These cams cooperate with contact lever 24 causing the lever to makecontact with arm 25 thereby closing the circuit I9, 20. As each of thecams 21 passes beyond the end of the contact lever 24, spring 28depresses the lever breaking the contact between the lever and contactarm 25 until the next cam cooperates with lever 24 as motor 26 continuesto rotate. Thus, since the synchronous motor will be in constantoperation, it will be seen that the electro-magnets l2, l2 will beperiodically deenerglzed and reenergized as long as the contacts 9 andID or III are closed. The timing of such energizing and deenergizing bymeans of the off and on relay 23 must, of course, be properly regulatedwith respect to the duration of the hunting period which otherwise mightbe estab lished. To this end the cams 21 are adjustable orinterchangeable as to their length and spacing so that the off and onperiods can be set as desired.

In Fig.4 there is illustrated a further modification of the device justexplained in connection with Fig. 3, for in this arrangement thesynchronous motor 26 is in operation only when the contacts 9 and ID oriii are closed, and the current to operate it is taken from the circuit2|, 22 instead of from the circuit i9, 20, as in Fig. 3. In thisembodiment the electro-magnets or solenoids l2, I2 have been providedwith a third set of contact discs 29, 29 each of which serves to closethe circuitcontrolling the operation of the synchronous motor 26. Thuswhen either one of the electro-magnets l2, I2 is energized the circuitof the motor 26 is completed through the contacts closed by disc 29 or29' respectively, and the feed-regulating motor M will operate as longas contacts 24, 25 are closed. However, when a cam 21 passes beyond theend of contact lever 24 the circuit 2|, 22 for the motor I4 istemporarily broken. When the next cam cooperates with lever 24, therebyclosing circuit 2|, 22, the motor I4 will again operate provided theelectro-magnets l2, l2 have not been deenergized through the opening ofcontacts 9 and ID or If). It is evident that the current which must bebroken by contacts 24, 25 will be greater in the arrangement of Fig. 4than in that of Fig. 3. In either arrangement the tendency towardover-correction or hunting will be avoided because the breaking andmaking of the control circuit by the oif-and-on relay device 23 isdependent-solely upon the operation of the synchronous motor 26 and itscams 21 and not in turn upon any other variable factor in the controlapparatus.

If the operation of the mill is to be controlled by the speed at whichit is driven the only alteration necessary in the arrangementsillustrated is to replace the regulator 6 of the driving motor of thefeed device by a regulator for a motor which drives the mill. Similarly,if the operation of the mill is to be controlled by the speed of the airstream through it, the regulator 6 may be replaced by a regulator of anelectric motor driving the fan, so that a reduction in the noise, i. e.an increase in the mill feed, brings about an increase in the fan speed.

Although it is convenient to drive the controlled device by an electricmotor and to adjust a regulator for that motor in accordance with thenoise, this is not essential. Thus the feed device may be driven fromthe mill through variable gearing that is adjusted in accordance withthe noise.

I claim:

A crushing or grinding mill in which the level of noise emitted by themill in operation is a function of the quantity of material therein, adevice for automatically controlling the operation of said millcomprising a microphone located near the mill to pick up said noise andtranslate it into audiofrequency current, an amplifier connected to saidmicrophone for increasing the level of said audio frequency current, afilter connected to the output of said amplifier, said filter beingadjustable to select those frequencies indicative of the quantity ofmaterial in the mill, contact means adjustably operative in response tocurrent of said selected frequencies to close one of two time-lag relayswhen said current reaches a preselected minimum or maximum value,respectively, means for adjusting said contact means to close atpreselected minimum and maximum values of current, two power relays eachcontrolled by one of said time-lag relays, a reversible motor-actuatedcontrolling device for said mill, an electric power source, contactsconnecting said power source to said motor upon operation of either ofsaid power relays, the direction of rotation of said motor beingdependent upon which 01' said power relays is operated, and anoiI-and-on relay device adjustably controlling the periods of operationof said motor independently of the other relays.

CARL FREDERIK QV'E RQDER.

